AR# 12758: sw4.1i PAR - Router incorrectly exits if timing score is zero, but there are still unrouted nets
sw4.1i PAR - Router incorrectly exits if timing score is zero, but there are still unrouted nets
Keywords: router, routing, unrouted, improving, hang
General Description: A problem was introduced in 4.1i wherein the router incorrectly exits after the first iteration when the timing score has reached zero, even if there are still unrouted nets.
This bug is in the base router, so it affects all device families. Design with no timing constraints are especially susceptible to this bug, because the auto-timespecing feature generates timing constraints that are easily met.
NOTE: In one case involving a Spartan device, the router appeared to hang after printing "Improving routing". This hang appears to be due to the unusual condition of running cleanup passes on a design with unrouted nets.